As one of modern secondary cells of high output and high energy density, a non-aqueous electrolyte secondary cell has come into use, the cell employing a non-aqueous electrolyte and offering a high electromotive force based on oxidization and reduction of lithium.
Such a non-aqueous electrolyte secondary cell generally employs a non-aqueous electrolyte wherein a solute of lithium salt, such as LiBF4 or LiPF6, is dissolved in an organic solvent such as ethylene carbonate or diethyl carbonate.
Unfortunately, the aforesaid organic solvent for use in the non-aqueous electrolyte is flammable, involving a fear of burning in abnormal operation such as overcharge. Hence, it has been a conventional practice in the art to provide a protection circuit such as to prevent the cell from being overcharged. This leads to a problem of cost increase.